Shanghai artist "Red" Hong Yi, enjoys finding all sorts of interesting ways to draw...without any traditional drawing utensils. She previously created a portrait of NBA icon Yao Ming by bouncing a basketball dipped in paint, and recently perfected a means of using the rings left by a coffee mug.
The results are incredibly detailed, and her ability to find contrast in the color values and intensity is amazing:
She says, "Quite a tricky medium to use...Too much water and the rings wouldn't form easily, very little water and you'd have to be precise with where you place the cup coz the rings would pretty much be permanent."
Red Hong's No Utensil Drawing Skills [Core77]